The invention relates generally to the chemical detection of halogenated hydrocarbons (halohydrocarbons) and more particularly to the detection of halohydrocarbons, including certain organic chlorides, using a Fujiwara-like reaction.
Trichloroethylene (TCE) heads the U.S. Environmental Protection Agency's (EPA) list of hazardous (toxic, carcinogenic, etc.) compounds and the organic chlorides, as a group, dominate the ten (10) most frequently found dangerous compounds. The other organic chlorides include 1,1,1-trichloroethane (TCA), 1,1,2,2-tetrachloroethane, chloroform (CHCl.sub.3), carbon tetrachloride (CCl.sub.4) and 1,2-dichloroethylene (DCE). Thus, the detection of these compounds is extremely important.
The Fujiwara reaction is a known methodology widely used for the fluorometric and colorimetric analysis of gem-polyhalogen compounds. In the presence of a strong alkali (OH.sup.-), such as sodium or potassium hydroxide, pyridine or a derivative thereof reacts with a halogenated hydrocarbon to produce a red colored fluorescent product. The traditional chemistry (pyridine/alkali metal base) is a two-phase system, since the commonly used aqueous alkalis (NaOH or KOH) are not miscible with pyridine. Therefore, the reaction product is formed only at the interface. The Fujiwara chemistry has been modified to overcome the limitations of the two-phase system. U.S. Pat. No. 4,929,562 to Anderson (deceased) et al. shows a single-phase system which utilizes pyridine or a derivative thereof with a hindered nitrogen base (phase transfer catalyst), particularly a tetra alkyl ammonium hydroxide (quaternary ammonium base). The organic bases (with bulkier counterions) have increased solubility in pyridine so that a single phase is achieved. However, in both cases above, the hydroxide ion serves as the base. The chemistry is usually species specific but not compound specific.
The detectable red reaction product using either the original Fujiwara chemistry or the chemistry as modified by Anderson is short lived and quickly converts to a light yellow final product which is difficult to detect. It is desirable to modify the sensing chemistry of Fujiwara or Anderson to overcome the deficiencies of the prior art and to produce a stable reaction product which is easy to detect.